Platinum (II) Di (2-Pyrazolyl) Benzene Chloride Analogs and Uses

ABSTRACT

Synthesis of platinum(II) di(2-pyrazolyl)benzene chloride and analogs includes forming a 1,3-di-substituted benzene including two aromatic five-membered heterocycles, and reacting the 1,3-di-substituted benzene with an acidic platinum-containing solution to form a luminescent platinum(II) complex. The luminescent platinum(II) complex is capable of emitting blue and white light and can be used as an emitter in a light emitting device.

PRIORITY CLAIM AND RELATED PATENT APPLICATION

This document claims priority from U.S. Patent Provisional ApplicationSer. No. 61/016,155 entitled “Platinum(II) Di(2-Pyrazolyl) BenzeneChloride Analogs and Uses” and filed on Dec. 21, 2007, the entirecontents of which are incorporated herein by reference as part of thedisclosure of this document.

TECHNICAL FIELD

This invention relates to platinum(II) di(2-pyrazolyl)benzene chlorideand analogs, and more particularly to the synthesis and use thereof.

BACKGROUND

As depicted in FIG. 1, an organic light-emitting device (OLED) 100 mayinclude a layer of indium tin oxide (ITO) as an anode 102, a layer ofhole-transporting materials (HTL) 104, a layer of emissive materials(EML) 106 including emitter(s) and host(s), a layer ofelectron-transporting materials (ETL) 108, and a metal cathode layer 110on substrate 112. The emission color of OLED 100 may be determined bythe emission energy (optical energy gap) of the emitter(s) in the layerof emissive materials. Phosphorescent OLEDs (i.e., OLEDs withphosphorescent emitters) may have higher device efficiency thanfluorescent OLEDs (i.e., OLEDs with fluorescent emitters). Some emittersfor blue phosphorescent OLEDs include iridium—a relatively scarceelement—in the form of cyclometalated iridium complexes.

SUMMARY

In one aspect, a luminescent compound has the generic formula

where

is an aromatic heterocycleand where W is —Cl or

The six-membered ring in this generic formula denotes benzene orpyridine.

In another aspect, a light emitting device includes the luminescentcompound shown above.

In certain implementations,

is selected from the group consisting of

In certain implementations, the luminescent compound is platinum(II)di(2-pyrazolyl)benzene chloride, with the formula:

In some implementations, the luminescent compound is phosphorescent. Thecompound is capable of emitting light in the blue range of the visiblespectrum. In some cases, the compound is capable of emitting whitelight. The light emitting device may be an organic light emittingdevice.

In another aspect, a method of making a platinum(II) complex includesforming a 1,3-di-substituted aromatic six-membered ring with twoaromatic five-membered heterocycles, and reacting the 1,3-di-substitutedsix-membered ring with an acidic platinum-containing solution to formthe platinum(II) complex.

In some implementations, the aromatic five-membered heterocycles areselected from the group consisting of pyrazolyl, substituted pyrazolyl,imidazolyl, substituted imidazolyl, thiazolyl, and substitutedthiazolyl. In certain implementations, the benzene is fluorinated,difluorinated, or methylated. Fluorinating the benzene ring may increasethe emission energy, shifting the emission toward the blue end of thevisible spectrum. The benzene may be bonded to a heteroatom, such as anitrogen atom or a sulfur atom, in the heterocycle. The platinum atom inthe platinum(II) complex may be bonded to a carbon atom and two nitrogenatoms. In some embodiments, the platinum(II) complex is platinum(II)di(2-pyrazolyl)benzene chloride. In certain implementations, thearomatic six-membered ring is benzene or pyridine. In some cases, whenthe six-membered ring is pyridine, an increase in the emission energymay result.

Phosphorescent blue OLEDs with the platinum complexes described hereinas emitters can be produced at low cost and provide operationally stabledisplays.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an organic light emitting device (OLED).

FIG. 2 shows precursors for platinum(II) di(2-pyrazolyl)benzene chlorideand analogs.

FIG. 3 shows platinum(II) di(2-pyrazolyl)benzene and analogs.

FIG. 4 shows a room temperature emission spectrum of platinum(II)di(2-pyrazolyl)benzene chloride in dichloromethane.

FIG. 5 shows room temperature and 77 K emission spectra of platinum(II)di(3,5-dimethyl-2-pyrazolyl)benzene chloride in solution.

FIG. 6 shows a room temperature emission spectrum of platinum(II)di(3,5-dimethyl-2-pyrazolyl)benzene chloride in thin film of poly(methylmethacrylate) (PMMA).

FIG. 7 shows a room temperature emission spectrum of platinum(II)di(3,5-dimethyl-2-pyrazolyl)benzene phenoxide in a thin film ofpoly(carbonate).

FIG. 8 shows a room temperature emission spectrum of platinum(II)di(3,5-dimethyl-2-pyrazolyl)toluene chloride in a thin film ofpoly(methyl methacrylate) (PMMA).

FIG. 9 shows a room temperature emission spectrum of platinum(II)di(methyl-imidazolyl)benzene chloride in a solution of dichloromethane.

FIG. 10 shows a room temperature emission spectrum of platinum(II)di(methyl-imidazolyl)benzene chloride in a thin film of poly(methylmethacrylate) (PMMA).

FIG. 11A shows a room temperature emission spectrum of platinum(II)di(methyl-imidazolyl)toluene chloride in a thin film of poly(methylmethacrylate) (PMMA).

FIG. 11B shows a 77 K emission spectrum of platinum(II)di(methyl-imidazolyl)pyridine chloride in a solution of2-methyl-tetrahydrofuran.

FIG. 12 shows a room temperature emission spectrum of platinum(II)di(thiazolyl)(4,6-difluoro-benzene) chloride in a solution ofdichloromethane.

DETAILED DESCRIPTION

The platinum complexes described herein can be used as emitters forOLEDs, absorbers for solar cells, luminescent labels forbio-applications, and the like. Blue phosphorescent OLEDs may includeplatinum complexes with high band-gap ligands, including thefive-membered rings depicted herein.

Platinum(II) di(2-pyrazolyl)benzene chloride and analogs may berepresented as:

in which:

is an aromatic heterocycle,

and W can be —Cl or

The aromatic six-membered ring in this generic formula denotes benzeneor pyridine. The aromatic five-membered heterocycle can be, for example,substituted pyrazolyl, imidazolyl, substituted imidazolyl, thiazolyl,and substituted thiazolyl ligands shown below:

In some embodiments, the luminescent compound is platinum(II)di(2-pyrazolyl)benzene chloride, shown below:

In some cases, the benzene ring is substituted, such as fluorinated ormethylated in one or more positions. Fluorinating the benzene ringincreases the emission energy, shifting the emission toward the blue endof the visible spectrum. In certain cases, the six-membered ring is apyridyl ring rather than benzene.

Platinum(II) di(2-pyrazolyl)benzene chloride and analogs describedherein may be prepared from the ligands depicted in FIG. 2. Synthesis ofthe ligands is described below.

HL¹: After standard cycles of evacuation and back-fill with dry and purenitrogen, an oven-dried Schlenk flask equipped with a magnetic stir barwas charged with Cu₂O (0.1 mmol, 10 mol %), syn-2-pyridinealdoxime (0.4mmol, 20 mol %), the pyrazole (2.5 mmol), Cs₂CO₃ (5.0 mmol), and the1,3-dibromobenzene (1.0 mmol), and anhydrous and degassed acetonitrile(20 mL). The flask was stirred in an oil bath, and refluxed for 3 days.The reaction mixture was allowed to cool to room temperature, dilutedwith dichloromethane and filtered through a plug of CELITE® (WorldMinerals Inc., Santa Barbara, Calif.), the filter cake being furtherwashed with dichloromethane (20 mL). The filtrate was concentrated undervacuo to yield a residue, which was purified by flash columnchromatography on silica gel to obtain the pure product HL¹ in 80%yield. ¹H NMR (CDCl₃): 6.51 (dd, 2H), 7.52 (t, 1H), 7.62 (dd, 2H), 7.76(d, 2H), 8.02 (d, 2H), 8.10 (s, 1H).

HL²: HL² was synthesized in 64% yield using the same procedure as HL¹except that 1,3-diiodobenzene was used as starting material. ¹H NMR(CDCl₃): 2.6 (s 12H), 6.0 (s, 2H), 7.42 (dd, 2H), 7.51 (t, 2H), 7.55 (t,2H).

HL³: 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene (1.0mmol), Pd(OAc)₂ (0.05 equiv), PPh₃ (0.2 equiv), 1-methyl-2-iodoimidazole(2.5 mmol) were resolved in dimethoxyethane/2M K₂CO₃ aqueous solution(20 mL, 1:1) under nitrogen atmosphere. The mixture was heated andrefluxed for 24 h. After being cooled to room temperature, the reactionmixture was diluted with EtOAc, and poured into a brine solution. Theorganic layer was separated, and washed with the water, dried, filtered,and the filtrate was concentrated under reduced pressure. The residuewas purified by column chromatography on silica gel to obtain the pureproduct HL³ in 34% yield. ¹H NMR (CDCl₃): 3.72 (s 6H), 7.12 (d, 2H),7.47 (t, 1H), 7.48 (d, 2H), 7.56 (s, 1H), 7.72 (d, 2H).

HL⁴: HL⁴ was synthesized in 40% yield using the same procedure as HL³except that1,3-difluoro-4,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzenewas used as starting material instead of1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-benzene. ¹H NMR(CDCl₃): 3.63 (s, 6H), 7.09 (t, 1H), 7.13 (d, 2H), 7.35 (t, 1H), 7.60(d, 2H).

HL⁵: HL⁵ was synthesized in 25% yield using the same procedure as HL³except that 2-bromothiozole was used as starting material instead of1-methyl-2-iodoimidazole. ¹H NMR (CDCl₃): 7.13 (t, 1H), 7.49 (d, 2H),7.98 (d, 2H), 9.23 (t, 1H).

HL⁶: HL⁶ was synthesized in 65% yield using the same procedure as HL¹except that imidazole was used as starting material. ¹H NMR (DMSO): 7.26(2H), 7.34 (2H), 7.41 (1H), 7.43 (2H), 7.62 (1H), 7.92 (2H).

HL⁷: Methyl iodide (3 equiv) was syringed into a 50 mL round-bottomedflask charged with HL⁶ (10 mmol) and DMSO (30 mL). The reaction wasstirred under nitrogen in room temperature for 48 h. The mixture waspoured into EtOAc (60 mL), and the white precipitate was formed,filtered, washed with ether, and air-dried to obtain HL⁷ in 85% yield.¹H NMR (DMSO): 3.99 (s, 6H), 7.97-8.00 (m, 3H), 8.00 (s, 2H), 8.31 (s,1H), 8.37 (s, 2H), 9.89 (s, 2H).

HL⁸: HL⁸ was synthesized in 60% yield using the same procedure as HL¹except that 1,3-diiodotoluene was used as starting material. ¹H NMR(CDCl₃): 2.28 (s, 6H), 2.32 (s, 6H), 2.44 (s, 3H), 5.98 (s, 2H),7.26-7.28 (m, 3H).

HL⁹: A mixture of 3,5-diiodotoluene (1.1 g, 3.0 mmol), 1-methylimidazole(7.5 mmol), Pd(OAc)₂ (5 mg, 0.01 mmol), KI (2.0 g, 12 mmol), and CuI(2.4 g, 12.2 mmol) in degassed DMF (12 mL) was heated under Ar at 140°C. for 10 days. After cooling to room temperature, the mixture waspoured into NH₃ solution (10%, 50 mL), and CH₂Cl₂ (40×3 mL) was added.The organic phase was separated and dried (MgSO₄), and the solvent wasevaporated. The crude product was purified by chromatograph (silica gel;ethyl acetate/methanol, 4:1) to give ligand HL⁹ as a light yellow solid(40%). ¹H NMR (CDCl₃): δ2.44 (s, 3H), 3.78 (s, 6H), 6.97 (d, 2H), 7.11(d, 2H), 7.52 (s, 2H), 7.60 (s, 1H).

HL¹⁰: HL¹⁰ was synthesized in 35% yield using the same procedure as HL¹except that 1,3-dibromopyridine was used as starting material. ¹H NMR(CDCl₃): 2.3 (s, 6H), 2.4 (s, 6H), 6.06 (s, 2H), 8.00 (t, 1H), 8.71 (d,2H).

HL¹¹: HL¹¹ was synthesized in 35% yield using the same procedure as HL⁹except that 1,3-dibromopyridine was used as starting material.

Pyridine-containing structures may be similarly synthesized.

Platinum(II) complexes were prepared from HL¹-HL¹¹ as described below.

Acetic acid (3 mL) and water (0.3 mL) were added to a mixture of theligand HL^(n) (e.g., 1.0 mmol) and K₂PtCl₄ (1 equiv) in a glass vesselwith a magnetic stir bar. The vessel was capped, and then the mixturewas heated under microwave irradiation for 30-60 minutes. Upon coolingto room temperature, a yellow or yellow-orange precipitate was formed.The precipitate was separated off from the yellow solution, washedsequentially with methanol, water, ethanol, and diethyl ether (e.g., 3×5mL of each), and dried under vacuum.

Platinum (II) Ligand chloride (PtL¹⁻¹¹Cl ) were treated with phenol andpotassium hydroxide in acetone to give PtL¹⁻¹¹OPh for 2-3 hs after beingfiltrated, washed by water, acetone, and ether.

FIG. 3 shows platinum(II) di(2-pyrazolyl)benzene chloride and analogssynthesized from the ligands. ¹H NMR data for these compounds in DMSO orCDCl₃ are listed below.

PtL¹Cl: ¹H NMR (DMSO): 6.84 (dd, 2H), 7.37 (t, 1H), 7.48 (d, 2H), 7.93(d, 2H), 8.91 (d, 2H).

PtL²Cl: ¹H NMR (DMSO): 2.62 (s, 6H), 2.72 (s, 6H), 6.32 (s, 2H),7.19-7.20 (m, 3H).

PtL³Cl: ¹H NMR (CDCl₃): 7.40 (dd, 2H), 7.28 (d, 2H), 7.13 (t, 1H), 6.93(d, 2H).

PtL⁵Cl: ¹H NMR (DMSO): 7.28 (t, 1H), 7.95 (d, 2H), 8.14 (d, 2H).

PtL⁸Cl: ¹H NMR (CDCl₃): 2.65 (s, 6H), 2.76 (s, 6H), 6.34 (s, 2H), 7.09(s, 2H).

PtL⁹Cl: ¹H NMR (CDCl₃): 7.37 (dd, 2H), 7.11 (d, 2H), 6.91 (d, 2H), 4.04(s, 6H), 2.34 (s, 3H).

PtL¹⁰Cl: ¹H NMR (CDCl₃): δ2.78 (s, 6H), 2.79 (s, 6H), 6.11 (s, 2H), 8.27(s, 2H).

PtL²OPh: ¹H NMR (CDCl₃): 7.07-7.16 (m, 5H), 7.02 (d, 2H), 6.49 (t, 1h),6.01 (s, 2H), 2.71 (s, 6H), 2.45 (s, 6H).

PtL²OPhBu-t: ¹H NMR (CDCl₃): 7.13 (t, 1H), 7.08 (d, 2H), 7.02 (d, 2H),7.00 (d, 2H), 6.00 (s, 2H), 2.71 (s, 6H), 2.47 (s, 6H), 1.25 (s, 9H).

PtL³OPh: ¹H NMR (CDCl₃): 7.23 (d, 2H), 7.17 (d, 2H), 7.11 (t, 1H), 7.06(t, 1H), 6.85-6.87 (m, 4H), 6.78 (d, 2H), 3.99 (s, 6H).

FIGS. 4-12 show photoluminescence spectra for several Pt complexesincluding PtL¹Cl, PtL²Cl, PtL³Cl, PtL⁵Cl, PtL⁸Cl, PtL⁹Cl, PtL¹¹Cl andPtL²OPh.

FIG. 4 shows a room temperature emission spectrum of platinum(II)di(2-pyrazolyl)benzene chloride in dichloromethane.

FIG. 5 shows room temperature (plot 500) and 77 K (plot 502) emissionspectra of platinum(II) di(3,5-dimethyl-2-pyrazolyl)benzene chloride insolution.

FIG. 6 shows a room temperature emission spectrum of platinum(II)di(3,5-dimethyl-2-pyrazolyl)benzene chloride in thin film of poly(methylmethacrylate) (PMMA).

FIG. 7 shows a room temperature emission spectrum of platinum(II)di(3,5-dimethyl-2-pyrazolyl)benzene phenoxide in a thin film ofpoly(carbonate).

FIG. 8 shows a room temperature emission spectrum of platinum(II)di(3,5-dimethyl-2-pyrazolyl)toluene chloride in a thin film ofpoly(methyl methacrylate) (PMMA).

FIG. 9 shows a room temperature emission spectrum of platinum(II)di(methyl-imidazolyl)benzene chloride in a solution of dichloromethane.

FIG. 10 shows a room temperature emission spectrum of platinum(II)di(methyl-imidazolyl)benzene chloride in a thin film of poly(methylmethacrylate) (PMMA).

FIG. 11A shows a room temperature emission spectrum of platinum(II)di(methyl-imidazolyl)toluene chloride in a thin film of poly(methylmethacrylate) (PMMA).

FIG. 11B shows a 77 K emission spectrum of platinum(II)di(methyl-imidazolyl)pyridine chloride in a solution of2-methyl-tetrahydrofuran.

FIG. 12 shows a room temperature emission spectrum of platinum(II)di(thiazolyl)(4,6-difluoro-benzene) chloride in a solution ofdichloromethane.

As seen in these spectra, these complexes provide the capability oftuning the emission energy of platinum(II) complexes over a rangebetween ultraviolet and near-infrared, as well as improved emission inthe blue wavelength range. These complexes can be used as luminescentlabels, emitters for OLEDs, and other applications that benefit fromefficient blue emission and high stability (longer lifetime).

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

1. A luminescent compound comprising:

wherein

is an aromatic heterocycle, and wherein W is —Cl or

2.-26. (canceled)